Investment Casting vs Die Casting: Which Method is Best for Your Needs?
Casting is one of the earliest and most traditional methods for manufacturing multiple parts of the same design. Although there are now several types of casting methods, they all still rely on the fundamental use of a cast on which liquid material is poured into and hardened.
In this article, we will be focusing on two of the most popular casting methods – investment casting and die casting. Although the outputs from both methods seem similar, they take very different approaches to creating a cast. How are they different and what should you consider when choosing between the two?
What is die casting?
Die casting is the more old-fashioned option and is a more “classical” casting technique. To more easily understand the die casting process, let us break it down into two steps:
- The mold used in die casting is typically machined from a block of hardened steel or high-strength alloy. This one-step process speeds up the turnaround time for the mold cavity. However, both the machining process and the material for the mold are expensive.
- Molten metal is forced into the cavity at high pressure. When the metal cools and solidifies, it is ejected from the mold and the process is repeated. With the appropriate material, the steel or alloy mold can be used to cast over a million parts before it needs to be repaired or replaced.
Die casting is quite traditional and is closer to what most people probably imagine when they hear about the casting method. Although reliable, it lacks the sophistication of the more innovative approach to casting.
What is investment casting?
Investment casting may seem like a more novel casting method, but it has also been around since ancient times. Its name is derived from the act of ‘investing’ materials on a master pattern to create a mold. The process has more steps and is innately more complex:
- Investment casting starts by making a master pattern. This is a prototype of the part to be reproduced created using wax. A cluster of master patterns can also be put together to create a wax sprue. Sprues are quite common for mass-scale reproduction.
- Refractory materials are applied to the master pattern. This is the step we refer to as investing. The most common refractory materials are silica, alumina, zircon, or aluminum silicates.
Investing is initially done by dipping the master pattern in a liquid s of the refractory material. Once this layer has dried, larger volumes of the refractory material are applied either by hand or by a rainfall spray mechanism.
This process is repeated until a layer at least 5 millimeters thick has been built. Silicate binders can also be mixed with the investment material to enhance mechanical strength. The mold is left to dry for at least 48 hours.
- Once the mold has hardened, the wax master pattern is removed by heating the mold and allowing the wax to flow out. This wax is often recovered and reused in commercial facilities. Any residual wax can be burned out by exposing the mold to temperatures ranging from 800 to 1000 °C.
- Molten metal is poured into the cast and allowed to harden. The mold is then broken apart and discarded to access the finished part.
With its multiple steps and the fact that molds are discarded after use, the investment casting process is a bit more involved and tedious. However, it excels in terms of surface finish and having tighter dimensional tolerances.
Which method should you use?
Both die casting and investment casting remain commercially valuable methods for manufacturing, particularly for high-strength steel or metal parts. However, they are distinct enough from each other that it’s fairly easy to identify situations where either die casting or investment casting is more beneficial.
Use die-casting if…
You need to produce a high volume of orders
Making a mold out of hardened steel is expensive and takes a lot of work. However, this mold can last even up to a million produced parts. If you’re anticipating handling orders at this magnitude, then the cost per piece of die-casting becomes very low.
You need quick turnaround times
Once the mold for die casting is ready, creating part becomes a simple and repetitive process that is perfectly suitable for automation. Nowadays, large-scale die casting facilities are still very common exactly because of how quickly they can churn out finished parts.
You’re working with large parts
Although it will require more complex and expensive machining, it is theoretically possible to create any part size with die casting. This is not the case for investment casting because the wax master pattern must be supported by a central sprue.
Use investment casting if…
You have low volume orders
While casting is generally used for large-scale production, investment casting is not economical when you’re dealing with several thousand parts. Investment casting is slow, tedious, and requires manual intervention at several points in the process. It may not require a huge capital cost but still has a higher cost per unit because of labor costs and production time.
You need prints with lots of details
Design freedom and level of detail are areas in which investment casting excels. Since you’re working with a wax master pattern, incorporating subtle design elements is easier. If you need to recreate a model with complex patterns and thin-walled features, your best bet would be to go into investment casting.
You’re working with both ferrous and non-ferrous metals
A major limitation of die casting is that its mold cannot be exposed to temperatures higher than the melting point of the mold material. This severely limits the materials that are compatible with die casting to mostly non-ferrous metals
Investment casting has no such restrictions. The refractory materials of investment casting can withstand whatever melting temperatures it is exposed to. This includes both ferrous and non0-ferrous materials.
Die casting and investment casting are both well-established casting methods. One is more apt for large-scale production while the other is more practical for producing at a slightly lower scale. As with any worthwhile choice, there are good and bad points for each option.
Die casting is a classic. Getting it started is expensive and a lot of work, but a single hardened steel mold is enough to jumpstart production at a large scale. On the other hand, investment casting succeeds in creating more detailed parts but is decidedly slower and more work-intensive. As is often the case in industrial processes, knowing the right tool for the job is key to success in casting.